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Novel materials of (E)-N'-(4-chlorobenzylidene)-4-hydroxybenzohydrazide (CBHB) and (E)-N'-(4-(diethylamino) benzylidene)-4-hydroxybenzohydrazide (DEABHB) were synthesized by condensation reaction process and solvent evaporation method was employed to grow CBHB and DEABHB single crystals at room temperature. Lattice parameters of CBHB and DEABHB compounds were recorded using single crystal X-ray diffraction method. The presence of functional groups of the synthesized CBHB and DEABHB compounds were confirmed by Fourier transform infrared and Fourier transform Raman spectral analyses. Various intermolecular interactions were studied using Hirshfeld surface analysis. Thermal stability of the hydrazone Schiff base compounds CBHB and DEABHB were studied by thermogravimetric and differential thermal analyses. Third order nonlinear optical properties of CBHB and DEABHB were measured using open aperature Z scan technique. Two photon absorption coefficient and optical limiting properties of the crystals were reported from the Z scan studies.

Perovskites compounds (ABO3) have found a great many applications due to the simplicity of the crystal structure, chemical composition, and synthesis methods. The properties of these compounds can be modified by doping at A or B sites. Pure and Ni-doped BaSnO3 perovskite materials have been synthesized by a solid-state technique. The x-ray diffraction pattern suggests the presence of a polycrystalline BaSnO3 cubic phase. Rietveld analysis was carried out with General Structure and Analysis System II software. A tiny nanorod-like growth pattern was observed when the Ni doping concentration is increased to 2 mol%. Raman analysis, x-ray photoelectron spectral studies, and electron spin resonance studies revealed the presence of oxygen vacancies. The substitution of tin by nickel ions and the presence of oxygen deficiency in the material can be the reason for the observed increase in magnetic moment with Ni doping. The nonlinear optical property obtained from the Z scan (open aperture) studies revealed the optical limiting nature of the synthesized samples. The observed nonlinear optical process in the prepared materials has potential applications in optical limiters and eye-protecting devices. The dielectric properties of the synthesized samples have also been investigated.

In this work, we demonstrate the importance of the free carrier absorption (FCA) process in the nonlinear optical absorption (NLA) behavior of carbonaceous nanomaterials synthesized by pyrolysis at...

ABO3 perovskites show unusual property modifications by proper substitution at the A and B sites. Polycrystalline perovskite BaSnO3 samples doped with different concentrations of manganese (BaSn1−xMnxO3) were synthesized by solid-state reaction method. Rietveld refinement of XRD analysis confirmed the structure and phase purity of the synthesized compound. Diamagnetic-to-paramagnetic transition and optical bandgap tuning indicate the substitutional effect of Mn in the host BaSnO3 lattice. The strong reverse saturable absorption of the synthesized samples makes them ideal candidate for optical limiting applications. The frequency and composition-dependent dielectric studies reveal that Mn-doped BaSn1−xMnxO3 can be used for high-frequency device applications. The cycling retention in the specific capacitance of 96.2% at a current density of 25 mA/g even after 2500 cycles in Mn-doped BaSnO3 electrode can be used in energy storage devices for supercapacitor applications.

Carbonaceous materials containing Fe/Fe3C(core)-graphite(shell) nanoparticles-embedded carbon globules and carbon nanotubes are synthesized using pyrolysis. The thickness of the graphitic shell on the Fe/Fe3C nanoparticles was varied by exposing Fe-acetylacetonate and toluene precursors to different initial temperatures (reaction tube insertion temperatures) Tin. Furthermore, the thickness of the graphitic layer and the degree of graphitization along with the defect concentration in the graphitic layer was controlled by this process. A proposed mechanism for the formation of such carbonaceous nanostructures due to variation of Tin is provided. Non-linear absorption (NLA) experiments were carried out to explore the effect of graphitization and the role of defects on the laser intensity dependent NLA behaviour of these samples. We demonstrate that degree of graphitization and defect concentration in the highly graphitized layers considerably enhances the NLA behaviour of high intensity laser radiation in the material. The enhancement of NLA coefficient is mainly attributed to the excited state absorption (ESA) and free carrier absorption (FCA) processes. Our results emphasize that the reported carbonaceous materials with optimum amount of defects in the graphitized framework are attractive for optical limiting in laser safety applications.

Pure and manganese chloride (MnCl2) doped l-arginine maleate dihydrate (LAMD) single crystals are synthesized by slow solvent evaporation technique. Three different doping concentrations are used for the study. The grown crystals are confirmed by single crystal X-ray analysis. Laser-induced breakdown spectroscopy is used to ascertain the presence of the dopant. The changes in the optical parameters of the pristine and doped LAMD crystals are analyzed using UV–Vis spectroscopy and photoluminescence technique. The nonlinear absorption coefficient of pure and doped crystals is determined using open aperture Z-scan technique. The variations in the dielectric constant, dielectric loss, ac conductivity and electronic polarizability of the crystal by doping are also studied. The changes in the thermal properties of the pure and doped LAMD crystals are studied using TGA–DTG and DSC analyses.

Nanostructured materials employed as passive nonlinear absorptive limiters offer protection to the human eyes and optical sensors from damage by pulsed laser radiation. However, such materials are prone to laser induced damage, which can be avoided or minimized by employing a robust shell layer. Here, we report the optical limiting properties of nine-atom silver quantum clusters grafted in TiO2 nanotube matrix (Ag9QCs-TNT). Nonlinear absorption revealed from open-aperture Z-scan measurements on Ag9QCs-TNT using both 5 ns (532 nm) and 100 fs (800 nm) laser pulses is larger than those observed from its pristine counterparts (Ag9QCs and TNT). The optical limiting threshold value obtained for Ag9QCs-TNT under fs excitation is smaller by a factor of five compared to that under ns excitation, indicating its ability to passively limit high intensity laser radiation for potential device applications.

In this work, an Ag nanoparticle colloidal suspension flowing in the form of a thin jet (250 μm) is irradiated by 150 femtosecond, 800 nm laser pulses to form a plasma which emits bremsstrahlung X-rays of up to 100 keV energy. The flowing jet ensures long-term durability of the plasma source during continuous laser irradiation. The laser pulse is p-polarized and the angle of incidence is normal to the jet surface, to optimize resonance absorption of laser radiation by the plasma electron density gradient. A 30-fold enhancement is observed in the X-ray yield in the nanoparticle suspension, compared to the precursor salt solution. This is because of the local field enhancement (LFE) associated with the localized surface plasmon resonance (LSPR) in Ag nanoparticles. Multiphoton ionization will be greatly enhanced in the presence of LFE, resulting in the generation of a relatively larger number of free electrons, which become “hot” electrons of high kinetic energy by resonance absorption. Bremsstrahlung in the X-ray regime occurs due to the deceleration of these hot electrons. Under identical excitation conditions the corresponding X-ray enhancement measured in Au nanoparticles is relatively lower at 18-fold. This decrease is due to the higher ionization potential of Au (9.22 eV) as compared to Ag (7.58 eV). On the other hand, absorption spectra and SEM images measured after continuous irradiation reveal that Au nanoparticles are more photostable compared to Ag nanoparticles. These studies show that Ag nanoparticles are better suited for X-ray generation compared to Au nanoparticles under the experimental conditions employed. Applications include dynamics studies, microscopy, and lithography.

KBiFe2O5 polycrystalline powder was synthesized via citrate assisted sol–gel route. Its structural, microstructural, linear, nonlinear optical and photocatalytic properties were investigated. X-ray diffraction analysis revealed its structure to be monoclinic phase at room temperature. Nonlinear optical absorption of this material was investigated using open aperture z-scan technique. A three-photon type absorption mechanism fitted well with the experimental data, and the corresponding nonlinear absorption coefficient was calculated to be 4 × 10−23 m3/W2. The band gap of this material as determined by diffuse reflectance spectroscopy was found to be 1.75 eV. This makes it suitable for visible light driven photocatalytic applications. The photocatalytic property of KBiFe2O5 was investigated by degradation of methylene blue under visible light irradiation at different pH. The degradation rate constant was found to be 0.031 min−1 at a pH of 11.

The nonlinear optical (NLO) material, 2-methyl-5-nitroaniline (M5NA), is synthesized and the crystals are grown by slow evaporation technique. The theoretical vibrational spectral analyses are done for the first time for M5NA using B3LYP computational method with the basis set cc-pVTZ. Natural Bond Orbital (NBO) and Atoms In Molecules (AIM) analyses are carried out for obtaining the charge transfer interactions and the Hirshfeld surface analysis with the fingerprint plot is performed for finding out the intermolecular interaction sites of the molecule. Using the theoretical and experimental IR and Raman spectra, the vibrations of M5NA are estimated. Changes in the linear and nonlinear optical properties with the addition of silver nanoparticles are studied from the UV–vis absorption spectra and the Z-Scan curves. A comparison of the hyperpolarizability values is done with pure and silver-added M5NA.

The slow solvent evaporation technique has been employed for the synthesis of l-arginine perchlorate (LAPCl) single crystals. The grown crystals are doped with 1, 2 and 3 mol% of MnCl2. The Powder X-ray Diffraction (PXRD) analysis confirmed that the pure and doped crystals belong to the orthorhombic crystal system with non-centrosymmetric space group P212121. The incorporation of dopants has been confirmed by Laser-Induced Breakdown Spectroscopy (LIBS) and Energy Dispersive X-ray Analysis (EDX). The modification in the linear optical properties has been analyzed by measuring the cut off wavelength, band gap, Urbach energy and the refractive index of the pure and doped crystals. The changes in the nonlinearity of the LAPCl have been studied by open aperture Z-scan technique and found that two-photon absorption (2PA) coefficient increased with increasing the dopant concentration. The dielectric properties, electronic polarizability and thermal properties of the pure and doped crystals are also studied.

Purpose: To report the intermediate-term safety and efficacy of Aurolab aqueous drainage implant (AADI) in patients with glaucoma. Methods: Retrospective review of patients who underwent AADI between January 2013 and December 2016. Patients aged >16 years and with a minimum follow-up of 6 months were included. Success was defined as complete when the intraocular pressure was ≥6 and ≤21 mmHg without antiglaucoma medication and as qualified if those requiring additional antiglaucoma medications were included. Results: The study included 55 patients (55 eyes) with a mean age ± standard deviation (SD) of 47.3 ± 18.1 years with a mean follow-up of 16.7 ± 11.4 months. Mean intraocular pressure reduced from 30.8 ± 11.1 mmHg to 13.1 ± 4.7, 14.1 ± 4.8, 15.7 ± 2.5 (P < 0.001) mmHg at 6 months, 1 year, and 2 years, respectively. The mean number of antiglaucoma medications reduced from 3.4 ± 1 to 0.8 ± 1.2, 0.7 ± 1.1, 0.8 ± 1 (P < 0.001) at 6 months, 1 year, and 2 years, respectively. The cumulative probability of complete and qualified success was 62% and 100% at 6 months, 54% and 92% at 1 year, and 43% and 88% at 2 years, respectively. Four patients failed during the follow-up period. Postoperative complication occurred in 28 eyes (51%), of which 17 eyes (31%) required intervention. Conclusion: AADI is a safe and effective treatment for the control of intraocular pressure in patients with glaucoma.

Herein, we have reported the alkyl and alkoxy phenylacetylene containing phenazine fused triphenylene discotic liquid crystals (DLCs) which are obtained by the condensation reaction of triphenylene-1,2-diquinone with 1,2-diamino-4,5-dibromobenzene, followed by Sonogashira C–C coupling reaction with 4-alkyl-phenylacetylene or 4-alkoxy-phenylacetylene. Six novel derivatives were synthesized and evaluated for their thermal and optical properties. They show a broad range of hexagonal columnar phase and retain their mesophase up to room temperature upon cooling from the isotropic liquid. Thermotropic liquid crystalline properties of all the compounds were studied by polarised optical microscopy (POM), differential scanning calorimetry (DSC). The self-assembly of mesophase structure was investigated by X-ray diffraction (XRD) studies. Thermogravimetric analysis of all the mesogens shows good thermal stability over a broad temperature range. The photophysical properties of newly synthesized compounds were measured using UV–Vis absorption and photoluminescence emission spectroscopy in anhydrous chloroform solvent. The π-extended conjugation in these mesogens exhibit strong absorption bands falling around 270–487 nm and corresponding emission band at 657–663 nm respectively. The high delocalization of π– electrons in extended discotic mesogens show high nonlinear optical properties when measured under excitation by nanosecond laser pulses at 532 nm. These materials may find distinctive applications in the semiconducting devices.

Hydrazone compound (E)-N′-[4-(dimethylamino) benzylidene]-4-hydroxybenzohydrazide hemihydrate (DMABHBH) was synthesized and single crystals of DMABHBH were grown by solvent evaporation method at room temperature. Molecular structure of DMABHBH compound was confirmed by 1H and 13C nuclear magnetic resonance techniques. The presence of functional groups was confirmed by Fourier transform infrared and FT Raman spectral analyses. The X-ray crystal structure was elucidated at 173 K by single crystal X-ray diffraction and the results were compared with the corresponding values obtained at 298 K. The compound crystallizes in the chiral monoclinic space group P21. Mechanical stability of the grown crystals was estimated from the Vicker’s microhardness test. Powder second harmonic generation efficiency of DMABHBH is about 1.1 times that of potassium dihydrogen phosphate. DMABHBH is found to show optical limiting behavior at high input light intensities, the third order nonlinear optical absorption coefficient measured using open aperture Z-scan studies, is 0.95 × 10−11 m/W. Anti-bacterial activity was studied using the well and disc diffusion methods.

The field of NLO grew substantially over the years, facilitating a deeper understanding of light-matter interaction and providing solutions for several technological problems. Efficient nonlinear optical interactions have become essential for many applications in advanced photonics. Obtaining materials with stronger nonlinear properties is an important step towards applications. Nanoparticles and nanocomposites have become important materials for nonlinear optics in recent years because of their interesting surface effects and properties such as quantum confinement, plasmon oscillations etc., The remarkable NLO properties displayed by nanomaterials have motivated the design and fabrication of nanoscale photonic and optoelectronic devices. In this chapter we will outline the physical origins of optical nonlinearity in material media, and discuss the nonlinear optical properties reported for advanced nanomaterials in recent years. Experimental techniques will be explained and results obtained in different nanomaterials will be overviewed.

Globular amorphous carbonaceous materials embedded with graphite encapsulated metallic Co-nanoparticles with a high degree of crystallinity are synthesized by pyrolysis and demonstrated as excellent candidates for optical limiters. The amount of metal precursor (Co-acetylacetonate) used with toluene for pyrolysis is chosen as a strategy to control the degree of graphitization of graphene-like shells around the embedded Co-nanoparticles and also the crystallinity of these Co nanoparticles in the samples. The graphitic shell with an optimum amount of defects tunes the electronic properties of these nanomaterials, providing the electronic states required for the enhancement of nonlinear optical absorption (NLA) through an excited state absorption (ESA) process. Simultaneously, the increase in the crystallinity of the Co nanoparticle enhances its metallic nature, which helps in increasing NLA performance through the free carrier absorption (FCA) process. The importance of highly metallic Co is to involve both the Co nanoparticle and its graphitic encapsulation in facilitating the FCA process, which substantially enhances NLA. In comparison with many similar samples (e.g., Fe3C@C at 100 μJ of laser energy), our present samples show superior NLA performance even at the much lower laser pulse energy of ∼15 μJ. This performance is much better than many of the present-day NLA materials too. The simple, low-cost and one-step pyrolysis synthesis process makes our materials even more attractive.

In this article we report acceleration observed for ions in a forward ablation geometry of 50 nm thick nickel film coated on a glass plate under nanosecond laser ablation. A detailed study with varying background pressure and laser energy of time of flight (TOF) spectra of ionic and other neutral transitions from plasma is undertaken. The results indicate that TOF spectra recorded for different neutral transitions exhibit different dynamical behavior (the slower peak of the neutral emission becomes faster with background pressure). Similar observation is seen for the ionic species as well. These observations have similarity to some of the reported double-layer concepts. However, the calculated electric fields from the acceleration appear to be anomalously higher. Along with the acceleration observed for the ionic and neutral lines, significant asymmetry in spectral shape is observed for neutral nickel line (712.2 nm) along with spectral broadening as the background pressure increases. This large asymmetry is indicative of micro electric fields present inside the laser produced plasma plume which may result in a continuous acceleration of ions. Interestingly, the asymmetry in spectral broadening exhibits temporal and spatial dependence which indicates that electric field is present in the plasma plume even for longer duration and also over a significant distance., Comment: The complete article uploaded

Laser surface structuring is a versatile physical method to alter the surface morphology and subsequent surface properties of solid materials. In this work, we report the role of ambient conditions in nanosecond laser (Nd:YAG laser, τ = 7 ns) surface texturing of silicon, and the optical and morphological characterization of textured samples. We performed multiscale texturing (5 mm × 5 mm) on silicon by keeping the target in air as well as in water. The significant differences in the morphological and optical properties of textured samples indicate that the ambience (air or water) has a crucial role in laser material processing. 3D topographical analysis shows that nanosecond laser texturing performed in air offers more roughness to the silicon surface, which results in much reduced optical reflection (R ≈ 10% in the visible region) from the textured surface. Laser texturing has numerous applications in material science, industry, and biomedical fields and our results indicate that materials with specific surface roughness and reflectivity can be fabricated by changing the ambient conditions of laser texturing.

Organic crystals of 2′,3,4,4′,5-pentamethoxy chalcone (PMC), grown by slow evaporation technique, are subjected to spectroscopic and nonlinear optical analyses. The experimental and theoretical vibrational spectra confirm that the charge-transfer interaction between the methoxy group and phenyl ring through the ethylenic bridge of the PMC molecule must be responsible for the simultaneous IR and Raman activation of C=C stretching and ring modes. The Natural Bond Orbital (NBO) and Atoms In Molecules (AIM) calculations verify the presence of intramolecular hydrogen bonding in the molecule. The large NLO efficiency predicted for PMC is confirmed for the first time by powder SHG efficiency experiment by Kurtz and Perry, while the third order nonlinearity is measured by means of open-aperture Z-scan technique. From the results, the use of PMC for nonlinear optical applications is suggested. The Surface Enhanced Raman Scattering (SERS) spectral investigations have been performed to obtain the adsorption geometry of PMC on the silver surface. Density functional theory at B3LYP/SDD level has been used to compute energies of different configurations of silver adsorbed-PMC to find their stability, optimized geometry of the most stable configuration, and for characterizations including vibrational, NBO and hyperpolarizability analyses.

A straightforward synthesis of novel phenazine fused triphenylene discotic liquid crystals (DLCs) is realized. The condensation of 3,4-diaminobenzoic acid with a triphenylene-1,2-diquinone intermediate gives an acid derivative which upon esterification with aliphatic alcohols produces the corresponding monomeric ester derivatives of the phenazine fused triphenylene discotic liquid crystals. The intermediate acid derivative exhibits a rectangular columnar phase along with a high isotropic phase transition temperature. However, the monomeric ester derivatives show a hexagonal columnar mesophase over a broad temperature range and stable when decreased to room temperature upon cooling from the isotropic phase. The mesomorphic properties of the acid and monomeric ester derivatives of the phenazine fused triphenylene DLCs were characterised by polarised optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction studies (XRD). The molecular structures of the intermediate and final compounds were characterised by spectral and elemental analysis. The photophysical properties of all the monomeric ester compounds were investigated in an anhydrous chloroform solvent and absorption bands around 291–472 nm and the corresponding emission bands at 658–661 nm were observed, respectively. The π-extended conjugation in these materials gives rise to high nonlinear optical properties. These materials have immense potential for use in electro-optical applications.

Novel EDOT based bent-core and hockey-stick shaped mesogens bearing terminal alkyl chains and alkoxy terminal chains, respectively, have been designed and synthesized via the Sonogashira coupling reaction. Molecular structures of these new compounds were determined using spectral and elemental analysis. The mesomorphic behaviour of all the novel compounds was primarily investigated by a combination of polarising optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction studies (XRD). All of the compounds exhibit an enantiotropic nematic phase in lower homologs. However, a smectic A phase at a lower temperature along with the high temperature nematic phase was observed in higher homologs of BC and hockey-stick LCs. A density functional theory study was carried out to investigate the stable configuration. The bent angle of these molecules was intermediate between calamitic LCs and banana LCs. The photophysical properties of all the compounds were studied in anhydrous chloroform solvent and show absorption patterns around 370–395 nm and emission between 418–465 nm. We have also reported large effective two-photon absorption in these novel compounds when measured under excitation by nanosecond laser pulses at 532 nm. All of the mesogenic compounds are nonlinear materials, which make them suitable candidates for optical limiting applications.

We report on enhanced nonlinear optical absorption and optical limiting in β-MnO2 sponge-like nanowire network decorated with Ag nanoparticles excited by nanosecond laser. A simple two-step process is used to prepare the samples. The structure, morphology and the elemental analysis of the prepared samples are studied using x-ray diffraction, field emission scanning electron microscopy and energy-dispersive x-ray spectroscopy. Nonlinear optical absorption properties of the samples in solution is studied using the open aperture Z-scan technique employing 5 ns laser pulses at 532 nm. Nonlinear transmission measurements show that β-MnO2 exhibit weak saturable absorption at low fluence and large optical limiting at high fluence, while upon decoration with Ag particles, Ag/β-MnO2 shows strong saturable absorption at low fluence and enhanced optical limiting at higher fluence with an optical limiting threshold value three times lower than that of bare β-MnO2 nanowires. The results indicate that these materials are potentially useful for constructing saturable absorbers and optical limiters.

Detailed investigations on the linear and nonlinear optical properties of 3‑chloro 4-fluoro aniline (CFA) and 2-iodo aniline (IA) have been carried out to understand their applicability. Natural Bond Orbital (NBO) analysis reveals the potential nonlinearity of CFA and IA by virtue of their π-conjugations in the carbon-ring systems and the n→σ* and n→π* hyperconjugations. Vibrational spectra of the molecules, investigated using the FT-IR and FT-Raman analyses, manifest the incidence of Fermi interaction and Evans hole in IA. The UV–vis spectral analysis brings out the fine photo response of CFA and IA in the visible region.The optical absorption technique has been employed to analyze the optical band gap of the title crystals, through the investigation of the absorption edge, to assess their effectiveness in optical devices.The z-scan measurement brings to light the remarkable third order nonlinearity in IA, with an extraordinary drop in normalized transmittance down to 39% at high laser fluences, which is a clear sign of its potential use as an optical limiter. A study of the molecular docking postures of CFA and IA ligands binding at the active sites of the target proteins reveal them suitable for use as therapeutic agents having anti-inflammation and anti-cancer activities against target proteins.

Benzylideneaniline compounds of N-(4-bromobenzylidene)-4-fluoroaniline (BBFA) and N-(4-bromobenzylidene)-4-methoxyaniline (BBMOA) have been synthesized by the condensation reaction process, and single crystals of these compounds are grown at room temperature by the slow evaporation solution growth technique. The compounds BBFA and BBMOA crystallize in the orthorhombic crystal system with different space groups. Placement of hydrogen atoms in BBFA and BBMOA compounds is confirmed from 1H NMR spectral studies. Fourier transform infrared and Raman spectral analyses are employed to study the presence of functional groups in the compounds. Single stage weight loss and melting point of these compounds are determined from thermogravimetric and differential thermal analyses respectively. Nonlinear optical properties are measured using powder second harmonic generation study and open aperture Z-scan technique. Biological activities are studied using the minimum inhibitory concentration method.

The interaction of pyrene on silver has been investigated using both experimental and computational methods. Hyperpolarizabilities computed theoretically together with experimental nonlinear absorption from open aperture Z-scan measurements, point towards a possible use of pyrene adsorbed on silver in the rational design of NLO devices. Presence of a red shift in both simulated and experimental UV–Vis spectra confirms the adsorption on silver, which is due to the electrostatic interaction between silver and pyrene, inducing variations in the structural parameters of pyrene. Fukui calculations along with MEP plot predict the electrophilic nature of the silver cluster in the presence of pyrene, with NBO analysis revealing that the adsorption causes charge redistribution from the first three rings of pyrene towards the fourth ring, from where the 2p orbitals of carbon interact with the valence 5s orbitals of the cluster. This is further confirmed by the downshifting of ring breathing modes in both the experimental and theoretical Raman spectra.

We report the nonlinear optical properties of graphene oxide (GO), reduced graphene oxide (rGO), sulfonated graphene oxide (S-rGO), and sparingly sulfonated water soluble graphene (WSG), measured under ultrafast (100 fs) and short pulse (300 ps, 50 ns) laser excitations at 800 nm, employing the open aperture Z-scan technique. The samples exhibit typical third order nonlinear optical behaviour including two-photon absorption (2 PA), reverse saturable absorption (RSA), and saturable absorption (SA). A significant variation in the nature of nonlinear absorption is seen when the laser pulse duration is changed. For example, RSA is prominent under nanosecond (ns) excitation, 2 PA is prevalent under femtosecond (fs) excitation, and SA is dominant under picosecond (ps) excitation. For comparison purposes the measurements are repeated using 5 ns laser pulses at 532 nm. RSA is enhanced in WSG in the nanosecond excitation domain, which can be attributed to the covalent bonding between p-phenyl-SO3H groups and sp2 graphitic planes. WSG exhibits a switching behaviour from SA to RSA upon increasing the excitation intensity under fs excitation. Results show that these graphene derivatives are potentially useful for saturable absorber and optical limiter device applications.

Photoluminescence properties and optical limiting behavior of pure and Sm 3+ /Eu 3+ doped Tb 2 (MoO 4 ) 3 nanophosphors are investigated. The prepared nanophosphors exhibit excellent emission when excited by UV light. Color-tunable emissions in Tb 2−x Sm x (MoO 4 ) 3 and Tb 2−x Eu x (MoO 4 ) 3 are realized by employing different excitation wavelengths or by controlling the doping concentration of Sm 3+ and Eu 3+ . Luminescence quantum yield and CIE chromatic coordinates of the prepared phosphors were also presented. Optical limiting properties of the samples are investigated by open aperture Z-scan technique using 5 ns laser pulses at 532 nm. Numerical fitting of the measured Z-scan data to the relevant nonlinear transmission equations reveals that the nonlinear absorption is arising from strong excited state absorption, along with weak absorption saturation and it is found that the optical nonlinearity of Tb 2 (MoO 4 ) 3 increases with Sm 3+ /Eu 3+ doping. Parameters such as saturation fluence, excited state absorption cross section and ground state absorption cross section of the samples have been determined numerically, from which the figure of merit for nonlinear absorption is calculated. The excited state absorption cross-section of the samples is found to be one order of magnitude higher than that of the ground state absorption cross-section, indicating strong reverse saturable absorption. These results indicate that Sm 3+ /Eu 3+ doped Tb 2 (MoO 4 ) 3 nanophosphors are efficient media for UV/n-UV pumped LEDs, and are also potential candidates for designing efficient optical limiting devices for the protection of human eyes and sensitive optical detectors from harmful laser radiation.

PURPOSE To compare the effect of mannitol in reducing intraocular pressure (IOP) in vitrectomized and nonvitrectomized eyes. MATERIALS AND METHODS Prospective comparative case study. Eyes with IOP≥40 mm Hg were included. Eyes which are vitrectomized and silicon oil filled were classified as group 1, and nonvitrectomized open-angle eyes were classified as group 2. Mannitol (20%, 1 g/kg) was administered intravenously over 30 minutes, and IOP was recorded at 30 minutes interval till 2 hours and at the third and fourth hour from the start of mannitol. RESULTS Thirty eyes (patients) were recruited in each group. Mean (SD) IOP reduced from 48.5±5.2 to 43.7±8 at 30 minutes, 40.7±8.4 at 60 minutes, 37.3±9.6 at 90 minutes, 35.6±10.4 at 2 hours, 34±10.7 at 3 hours, and 33±11.2 mm Hg at 4 hours in group 1, and from 48.9±6.5 to 43.2±8.6 at 30 minutes, 40.2±7.8 at 60 minutes, 36.7±7.3 at 90 minutes, 35.1±7.7 at 2 hours, 34.2±8.8 at 3 hours, and 35.7±9.4 mm Hg at 4 hours in group 2. There was a significant reduction in IOP at each time point compared with baseline in both the groups (P

A series of MnxZn1-xO (x=0.03, 0.05) nanostructures have been grown via the solution based chemical spray pyrolysis technique. Electron beam induced modifications on structural, linear and nonlinear optical and surface morphological properties have been studied and elaborated. GXRD (glancing angle X-ray diffraction) patterns show sharp diffraction peaks matching with the hexagonal wurtzite structure of ZnO thin films. The upsurge in ebeam dosage resulted in the shifting of XRD peaks (101) and (002) towards lower angle side, and increase in FWHM value. Gaussian deconvolution on PL spectra reveals the quenching of defect centers, implying the role of electron beam irradiation regulating luminescence and defect centers in the nanostructures. Irradiation induced spatial confinement and phonon localization effects have been observed in the films via micro Raman studies. The later are evident from spectral peak shifts and broadening. Detailed investigations on the effect of electron beam irradiation on third order nonlinear optical properties under continuous and pulsed mode of laser operation regimes are deliberated. Third order absorptive nonlinearity of the nanostructures evaluated using the open aperture Z-scan technique in both continuous and pulsed laser regimes shows strong nonlinear absorption coefficient β eff of the order 10-4 cm/W confirming their suitability for passive optical limiting applications under intense radiation environments. Laser induced third harmonic generation (LITHG) experiment results supports the significant variation in nonlinearities upon electron beam irradiation, and the effect can be utilized for frequency conversion mechanisms in high power laser sources and UV light emitters

Development of tunable photonic devices having molecular dimensions is an active research area in nonlinear optics which continues to evolve and impact many technologies. Here, we demonstrate the tailoring of nonlinear optical properties of nitrochalcone derivatives by engineering the donor-acceptor configurations on either end of the molecules, to control the intramolecular charge transfer process. The central π-bridge in chalcones provides delocalized electrons which lead to the nonlinear polarizability observed in these molecules. Optical nonlinearity is studied by means of second harmonic generation (SHG) and open aperture Z-scan measurements. Samples show optical limiting behaviour in the nanosecond excitation regime due to excited state absorption (ESA) and two-photon absorption (2PA) phenomena. Our study highlights the importance of structure-property correlations in molecular designs.